Fix jdbc-v2: build the getMetaData DESCRIBE query from the parser's placeholder positions

CHANGELOG.md

@@ -101,6 +101,13 @@
 
 ### Bug Fixes 
 
+- **[jdbc-v2]** Fixed `PreparedStatement.getMetaData()` losing the result-set schema for a statement whose SQL
+  contains a comment. The `DESCRIBE` query used to resolve the metadata was built by re-scanning the SQL with a
+  regex that knew only quoted tokens, so a `?` inside a `--` / `#` / `/* */` comment was rewritten to `NULL` and
+  an odd `'` inside a comment mis-paired the quote alternative, leaving a real placeholder unreplaced — the
+  `DESCRIBE` then failed and the driver silently returned untyped metadata. The metadata query is now built from
+  the placeholder positions the statement parser already computed, so it always matches the SQL that a
+  parameterized execution produces. (https://github.com/ClickHouse/clickhouse-java/issues/3011)
 - **[client-v2]** Fixed reading a `UInt64` column into a **primitive** POJO field (e.g. `long`) always failing with
   `ClassCastException: BinaryStreamReader cannot be cast to java.math.BigInteger`. The compiled setter for that
   combination never emitted a read call, so it cast the reader itself instead of a value and consumed nothing from the

jdbc-v2/src/main/java/com/clickhouse/jdbc/PreparedStatementImpl.java

@@ -131,6 +131,18 @@ private String buildSQL() throws SQLException {
         return compiledSql.toString();
     }
 
+    private String substituteParameters(String value) {
+        StringBuilder compiledSql = new StringBuilder(originalSql);
+        int posOffset = 0;
+        int[] positions = parsedPreparedStatement.getParamPositions();
+        for (int i = 0; i < argCount; i++) {
+            int p = positions[i] + posOffset;
+            compiledSql.replace(p, p + 1, value);
+            posOffset += value.length() - 1;
+        }
+        return compiledSql.toString();
+    }
+
     @Override
     public ResultSet executeQuery() throws SQLException {
         ensureOpen();
@@ -411,7 +423,7 @@ public ResultSetMetaData getMetaData() throws SQLException {
             if (parsedPreparedStatement.isHasResultSet()) {
                 try {
                     // Replace '?' with NULL to make SQL valid for DESCRIBE
-                    String sql = replaceQuestionMarks(originalSql, NULL_LITERAL);
+                    String sql = substituteParameters(NULL_LITERAL);
                     TableSchema tSchema = connection.getClient().getTableSchemaFromQuery(sql);
                     resultSetMetaData = new ResultSetMetaDataImpl(tSchema.getColumns(),
                             connection.getSchema(), connection.getCatalog(),

jdbc-v2/src/test/java/com/clickhouse/jdbc/PreparedStatementTest.java

@@ -1775,6 +1775,30 @@ public void testParameterCount() throws Exception {
         }
     }
 
+    @Test(dataProvider = "testGetMetadataIgnoresCommentsDataProvider")
+    public void testGetMetadataIgnoresComments(String sql) throws Exception {
+        try (Connection conn = getJdbcConnection();
+             PreparedStatement stmt = conn.prepareStatement(sql)) {
+            ResultSetMetaData metaData = stmt.getMetaData();
+            assertEquals(metaData.getColumnCount(), 3);
+            assertEquals(metaData.getColumnName(1), "x");
+            assertEquals(metaData.getColumnName(2), "y");
+            assertEquals(metaData.getColumnName(3), "z");
+            assertEquals(metaData.getColumnType(1), Types.VARCHAR);
+            assertEquals(metaData.getColumnType(3), Types.VARCHAR);
+        }
+    }
+
+    @DataProvider(name = "testGetMetadataIgnoresCommentsDataProvider")
+    static Object[][] testGetMetadataIgnoresCommentsDataProvider() {
+        return new Object[][] {
+                {"SELECT 'a' AS x -- it's ?\n, ? AS y, 'z' AS z"},
+                {"SELECT 'a' AS x # it's ?\n, ? AS y, 'z' AS z"},
+                {"SELECT 'a' AS x /* it's ? */, ? AS y, 'z' AS z"},
+                {"SELECT 'a?b' AS x, ? AS y, 'z' AS z"}
+        };
+    }
+
     @Test
     public void testEncodingArray() throws Exception {
         try (Connection conn = getJdbcConnection();) {